Solid-state imaging element, imaging device, and electronic device

ABSTRACT

The present technology relates to a solid-state imaging element, an imaging device, and an electronic device that can improve transfer efficiency of a charge accumulation unit (MEM) and can increase the number of saturation electrons Qs. In a case where a charge voltage conversion unit (FD) is connected to a center of a charge accumulation unit (MEM) in each pixel and pixels are arrayed in an array, a column in which photoelectric conversion units (PD) are arrayed and a column including charge voltage conversion units (FD) and pixel transistors are arrayed in parallel. The present technology can be applied to a CMOS image sensor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase of International PatentApplication No. PCT/JP2016/056728 filed on Mar. 4, 2016, which claimspriority benefit of Japanese Patent Application No. JP 2015-054326 filedin the Japan Patent Office on Mar. 18, 2015. Each of theabove-referenced applications is hereby incorporated herein by referencein its entirety.

TECHNICAL FIELD

The present technology relates to a solid-state imaging element, animaging device, and an electronic device and specifically relates to asolid-state imaging element, an imaging device, and an electronic devicethat can improve charge transfer efficiency and increase the number ofsaturation electrons Qs.

BACKGROUND ART

Conventionally, a complementary metal oxide semiconductor (CMOS) imagesensor (CIS) in which a photoelectric conversion unit (photodiode: PD),a charge accumulation unit (MEM), a floating diffusion (FD), and a pixelTr. (transistor) are formed in an own pixel region and a pixel array isformed has been proposed (see Patent Document 1).

In such a complementary metal oxide semiconductor (CMOS) image sensor(CIS) including a charge accumulation unit (MEM) in a pixel, the chargeaccumulation unit (MEM) is arranged in an own pixel region, and a changeaccumulated in the charge accumulation unit (MEM) is transferred to acharge voltage conversion unit (floating diffusion: FD).

CITATION LIST Patent Document

Patent Document 1: Japanese Patent Application Laid-Open No. 2013-254805

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in the above-described conventional art, in a case where acharge accumulation unit (MEM) is arranged in an own pixel region and acharge voltage conversion unit (FD) is arranged in a manner of beingconnected to a position other than a center of the charge accumulationunit (MEM), a transfer distance from an outer peripheral part of thecharge accumulation unit (MEM) to the charge voltage conversion unit(FD) becomes long, and there is a possibility that a transfercharacteristic is deteriorated.

Also, it is necessary to increase the number of masks of an implant andto forma sufficient potential gradient in order to perform a goodtransfer for a long transfer distance. Thus, the number of masks and thenumber of times of implantation are increased and a man-hour isincreased.

Furthermore, it is not possible to make a potential deep in an outerperipheral part of the charge voltage conversion unit (FD) concerning atransfer gradient. Thus, the number of saturation electrons in a unitarea is decreased as a transfer distance becomes long.

The present technology is provided in view of such a situation and isspecifically to improve charge transfer efficiency and to increase thenumber of saturation electrons Qs.

Solutions to Problems

A solid-state imaging element of an aspect of the present technologyincludes: a pixel including a photoelectric conversion unit thatgenerates a charge by photoelectric conversion according to an amount ofincident light, a charge accumulation unit that accumulates the chargegenerated by the photoelectric conversion unit, a charge voltageconversion unit that converts the charge accumulated in the chargeaccumulation unit into voltage, and a pixel transistor that outputs apixel signal on the basis of the voltage converted by the charge voltageconversion unit, in which in a case where the charge voltage conversionunit is connected to a center of the charge accumulation unit and pixelsare arrayed in an array, a column including photoelectric conversionunits and a column including voltage conversion units and pixeltransistors are formed in parallel.

A plurality of electrodes that forms a transfer gradient to transfer thecharge accumulated in the charge accumulation unit is further included,in which a recess is provided at a center of each of the plurality ofelectrodes in such a manner as to face the charge voltage conversionunit, an electrode in an outermost periphery being formed in such amanner as to surround, in the recess, a different electrode smaller thanthe electrode in the outermost periphery, the different electrode beingformed in such a manner as to surround, in the recess, a differentelectrode smaller than the different electrode, and an electrodeconnected to the charge voltage conversion unit being formed in therecess of the smallest electrode.

The thicknesses of the plurality of electrodes may be even.

The thicknesses of the plurality of electrodes may be uneven.

The plurality of electrodes may be configured with a small number ofthick electrodes as a margin in the transfer gradient in the chargeaccumulation unit becomes large, and may be configured with a largenumber of thin electrodes as the transfer gradient becomes insufficient.

An imaging device of an aspect of the present technology includes: apixel including a photoelectric conversion unit that generates a chargeby photoelectric conversion according to an amount of incident light, acharge accumulation unit that accumulates the charge generated by thephotoelectric conversion unit, a charge voltage conversion unit thatconverts the charge accumulated in the charge accumulation unit intovoltage, and a pixel transistor that outputs a pixel signal on the basisof the voltage converted by the charge voltage conversion unit, in whichin a case where the charge voltage conversion unit is connected to acenter of the charge accumulation unit and pixels are arrayed in anarray, a column including photoelectric conversion units and a columnincluding voltage conversion units and pixel transistors are formed inparallel.

An electronic device of an aspect of the present technology includes: apixel including a photoelectric conversion unit that generates a chargeby photoelectric conversion according to an amount of incident light, acharge accumulation unit that accumulates the charge generated by thephotoelectric conversion unit, a charge voltage conversion unit thatconverts the charge accumulated in the charge accumulation unit intovoltage, and a pixel transistor that outputs a pixel signal on the basisof the voltage converted by the charge voltage conversion unit, in whichin a case where the charge voltage conversion unit is connected to acenter of the charge accumulation unit and pixels are arrayed in anarray, a column including photoelectric conversion units and a columnincluding voltage conversion units and pixel transistors are formed inparallel.

One aspect of the present technology includes a pixel in which a chargeis generated by photoelectric conversion by a photoelectric conversionunit according to an amount of incident light, the charge generated bythe photoelectric conversion unit is accumulated by a chargeaccumulation unit, the charge accumulated in the charge accumulationunit is converted into voltage by a charge voltage conversion unit, anda pixel signal is output by a pixel transistor on the basis of thevoltage converted by the charge voltage conversion unit. In a case wherethe charge voltage conversion unit is connected to a center of thecharge accumulation unit and pixels are arrayed in an array, a columnincluding photoelectric conversion units and a column including voltageconversion units and pixel transistors are formed in parallel.

Effects of the Invention

According to one aspect of the present technology, it becomes possibleto improve charge transfer efficiency and to increase the number ofsaturation electrons Qs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view for describing a configuration of a pixel of a generalsolid-state imaging element.

FIG. 2 is a view for describing a configuration of a pixel transferefficiency of which is improved as compared with that of the pixel inFIG. 1.

FIG. 3 is a view for describing a configuration in a case where pixelsin FIG. 2 are arranged in an array.

FIG. 4 is a view for describing a configuration example of oneembodiment of a pixel of a solid-state imaging element to which thepresent technology is applied.

FIG. 5 is a view for describing a configuration in a case where pixelsin FIG. 4 are arranged in an array.

FIG. 6 is a view for describing a configuration example of a chargeaccumulation unit.

FIG. 7 is a view for describing that the amount of saturation electronscan be increased.

FIG. 8 is a view for describing a configuration of a light shieldingfilm in the pixel in FIG. 4.

FIG. 9 is a view for describing a configuration of a light shieldingfilm in a case where an electrode of the charge accumulation unit has aplate shape without a recess at a center.

FIG. 10 is a block diagram for describing a configuration of an imagingdevice and an electronic device using a solid-state imaging element towhich the present technology is applied.

FIG. 11 is a view illustrating an example of usage of the solid-stateimaging element.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, an example of the best mode for carrying out thepresent invention will be described. However, the present invention isnot limited to the following example.

<Configuration Example of Pixel of General Solid-State Imaging Element>

FIG. 1 is a view illustrating a configuration example of a pixel in ageneral solid-state imaging element including a complementary metaloxide semiconductor (CMOS) image sensor (CIS).

A pixel 11 in FIG. 1 includes a photoelectric conversion unit(photodiode: PD) 21, a charge accumulation unit (MEM) 22, a transfertransistor (TRG) 23, a charge voltage conversion unit (floatingdiffusion: FD) 24, and a pixel transistor (reset transistor RST andamplification transistor AMP) 25. Note that FIG. 1 is a top view of apixel.

As illustrated in FIG. 1, in the drawing, the charge accumulation unit(MEM) 22 is arranged on the photoelectric conversion unit (PD) 21, thecharge voltage conversion unit (FD) 24 is provided on a left sidethereof, and a charge is transferred via the transfer transistor (TRG)23 in a layout of the pixel 11.

With such a configuration, as indicated with an upward arrow, chargesgenerated according to the amount of incident light in the photoelectricconversion unit (PD) 21 are transferred to the charge accumulation unit(MEM) 22 and serially accumulated. Then, the charges accumulated in thecharge accumulation unit (MEM) 22 are transferred to the charge voltageconversion unit (FD) 24 via the transfer transistor (TRG) 23 asindicated by an arrow in a left direction.

Here, since the charge accumulation unit (MEM) 22 is arranged in an ownpixel region and the charge voltage conversion unit (FD) 24 is arrangedat a position other than a center of the charge accumulation unit (MEM)22, a transfer distance, for example, from a right end part of thecharge accumulation unit (MEM) 22 in the drawing to the charge voltageconversion unit (FD) 24 becomes long.

That is, as illustrated in a left part of FIG. 2, in a case where thecharge voltage conversion unit (FD) 24 is provided at an upper right ofthe charge accumulation unit (MEM) 22, it is necessary to move thelongest distance indicated by an arrow from a lower left to the upperright of the charge accumulation unit (MEM) 22. Thus, there is apossibility that a transfer characteristic is deteriorated.

Note that in the left part of FIG. 2, the charge voltage conversion unit(FD) 24 is connected to the upper right part of the charge accumulationunit (MEM) 22, the pixel transistor 25 is provided at an upper of thecharge voltage conversion unit (FD) 24 in the drawing, and thephotoelectric conversion unit (PD) 21 is provided at the lower left partof the charge accumulation unit (MEM) 22. Since such a pixel 11 on theleft part of FIG. 2 are arranged in an array, a column in whichphotoelectric conversion units 21 are provided and a column in whichpixel transistors 25 are provided can be in parallel in a verticaldirection. Thus, photoelectric conversion units (PD) 21 can be arrangedin a grid.

In a case of such a configuration, it is considered to increase thenumber of masks of an implant and to form a sufficient transfer gradient(potential gradient) in order to perform a good transfer for a longtransfer distance of the charge accumulation unit (MEM) 22.

However, in this case, the number of masks and the number of times ofimplantation are increased and a man-hour is increased. Also, concerninga transfer gradient, it is not possible to form a potential deeply in apart of the charge accumulation unit (MEM) 22 which part is the farthestfrom a part where the charge voltage conversion unit (FD) 24 isconnected. Thus, the number of saturation electrons in a unit area isdecreased markedly as a transfer distance becomes long.

Thus, in order to reduce deterioration of a transfer characteristic, alayout of shortening the longest transfer distance in the chargeaccumulation unit (MEM) 22 to the charge voltage conversion unit (FD) 24by connecting the charge voltage conversion unit (FD) 24 to an uppercenter of the charge accumulation unit (MEM) 22 is considered asindicated by a pixel 11′ on a right side of FIG. 2.

That is, as illustrated in the right part of FIG. 2, a position of thecharge voltage conversion unit (FD) 24 is arranged at the upper centerof the charge accumulation unit (MEM) 22, whereby the transfer distancein the charge accumulation unit (MEM) 22 becomes a distance from a lowerend part in a horizontal direction to the upper center at the longest.Thus, it is possible to shorten the transfer distance as a whole and tocontrol reduction of the transfer characteristic. However, in this case,as illustrated in FIG. 3, in a case of arranging a plurality of pixels11′ in an array on a plane, it is not possible to make a column in whichphotoelectric conversion units (PD) 21 are provided and a column, inwhich pixel transistors 25 are provided, to be columns in a verticaldirection.

That is, an example in which pixels 11′-1 to 11′-11 are serially arrayedis illustrated in FIG. 3. A column in which photoelectric conversionunits (PD) 21 are provided and a column in which charge voltageconversion units (FD) 24 and pixel transistors 25 are provided cannot beformed in parallel with the vertical direction and the photoelectricconversion units (PD) 21 cannot be arranged regularly. Thus, a pixellayout including a wiring line becomes complicated.

<Configuration Example of Pixel of Solid-State Imaging Element to whichPresent Technology is Applied>

Next, a configuration example of a pixel of a solid-state imagingelement to which the present technology is applied will be describedwith reference to FIG. 4.

As illustrated in FIG. 4, a pixel 51 to which the present technology isapplied includes a photoelectric conversion unit (PD) 71, a chargeaccumulation unit (MEM) 72, a charge voltage conversion unit (FD) 73,and a pixel transistor (pixel Tr.) 74. Note that the photoelectricconversion unit (PD) 71, the charge accumulation unit (MEM) 72, thecharge voltage conversion unit (FD) 73, and the pixel transistor (pixelTr.) 74 respectively correspond to the photoelectric conversion unit(PD) 21, the charge accumulation unit (MEM) 22, the charge voltageconversion unit (FD) 24, and the pixel transistor (pixel Tr.) 25 in FIG.2.

As illustrated in FIG. 4, the charge voltage conversion unit (FD) 73 isconnected to an upper center of the charge accumulation unit (MEM) 72 inthe pixel 51. Thus, since the longest one among transfer distances ofcharges accumulated in the charge accumulation unit (MEM) 72 to thecharge voltage conversion unit (FD) 73 can be minimized, it becomespossible to control reduction in transfer efficiency.

Note that a transfer transistor 84 (FIG. 6) is provided between thecharge accumulation unit (MEM) 72 and the charge voltage conversion unit(FD) 73. Charges accumulated in the charge accumulation unit (MEM) 72are transferred to the charge voltage conversion unit (FD) 73 via thistransfer transistor 84 (FIG. 6).

Furthermore, the photoelectric conversion unit (PD) 71 and the chargeaccumulation unit (MEM) 72 are connected in a positional relationship inwhich the photoelectric conversion unit (PD) 71, the charge voltageconversion unit (FD) 73, and the pixel transistor (pixel Tr.) 74 are notoverlapped in the vertical direction.

With such a configuration, a plurality of pixels 51 can be arrayed insuch a manner that photoelectric conversion units (PD) are in an arrayin a horizontal direction and a vertical direction as illustrated inFIG. 5. A pixel 51-5 in FIG. 5 is arranged in such a manner that aphotoelectric conversion unit (PD) 71 of a pixel 51-2 thereabove is fitin a space at an upper left of a charge accumulation unit (MEM) 72.Also, the arrangement is performed in such a manner that a chargevoltage conversion unit (FD) 73 and a pixel transistor (Tr.) 74 of apixel 51-8 thereunder are fit in a space at a lower right of the chargeaccumulation unit (MEM) 72 of the pixel 51-5. Furthermore, thearrangement is performed in such a manner that a part, which isprotruded to a right side, of the charge accumulation unit (MEM) 72 ofthe pixel 51-5 adjacent on a left side is fit in a space at a left endpart of the charge accumulation unit (MEM) 72 of the pixel 51-5. Also,the arrangement is performed in such a manner that a part, which isprotruded to the right side, of the charge accumulation unit (MEM) 72 ofthe pixel 51-5 is fit in a space at a left end part of a chargeaccumulation unit (MEM) 72 of a pixel 51-6 adjacent on the right side.

The other pixels 51 are arranged similarly, whereby the photoelectricconversion units (PD) 71 of the pixels 51 can be arranged in an array.

As illustrated in FIG. 4, since the pixels 51 are arranged in an array,a column L1 including the photoelectric conversion units (PD) 71, and acolumn L2 including the charge voltage conversion units (FD) 73 and thepixel transistors (pixel Tr.) 74 are configured as columns in parallelin the vertical direction.

As a result, as indicated by the pixels 51-1 to 51-9 in FIG. 5, thephotoelectric conversion units (PD) 71 of three pixels×three pixels canbe regularly laid out in a grid. Also, since it becomes possible toconfigure a wiring line along each of the columns L1 and L2 of thecolumn L1 including the photoelectric conversion units (PD) 71 and thecolumn L2 including the charge voltage conversion units (FD) 73 and thepixel transistors (pixel Tr.) 74, it becomes possible to simplifyrouting of the wiring line.

<Configuration of Electrode to Transfer Charge of Charge AccumulationUnit (MEM)>

Next, a configuration of an electrode that transfers a charge of theabove-described charge accumulation unit (MEM) 72 will be described withreference to FIG. 6. That is, as illustrated in FIG. 6, an electrodethat transfers a charge of the charge accumulation unit (MEM) 72 has aconfiguration in which box-shaped electrodes 81 to 83 with a recessbeing provided at an upper part from a lower part in the drawing. Anelectrode of the transfer transistor 84 is provided in the recess of thesmallest electrode 83, which is laminated on the uppermost part and isprovided with the smallest recess, and connection to the charge voltageconversion unit (FD) 73 is made via this transfer transistor 84. Notethat FIG. 6 is a top view of the pixel 51, the electrodes 81 to 83 ofthe charge accumulation unit (MEM) 72 and the transfer transistor 84being expressed in a sectional view seen in a top surface direction.

That is, each of the electrodes 81 to 83 is a box-shaped electrode witha recess being provided on an upper side in the drawing. The electrode82 is laminated in the recess of the electrode 81, the electrode 83 islaminated in the recess of the electrode 82, and the electrode of thetransfer transistor 84 is laminated in the recess of the electrode 83.The plurality of electrodes that transfers a charge of the chargeaccumulation unit (MEM) 72 is formed in a square shape as a whole. Inother words, the electrodes 81 to 83 that transfer a charge of thecharge accumulation unit (MEM) 72, and the transfer transistor 84 have aconfiguration in which the electrodes 81 to 83 are concentricallylaminated with a center being an upper center to which the chargevoltage conversion unit (FD) 73 that is a transfer direction of a chargeis connected.

With such a configuration, it becomes possible to configure a transfergradient in each of the electrodes 81 to 83. Thus, it becomes possibleto increase the number of saturation electrons Qs as compared with acase where electrodes 81 to 83 are one electrode as a whole.

That is, in a case where a charge accumulation unit (MEM) 72 as a wholeis one electrode 85, it is necessary to set a transfer gradient for awhole charge transfer distance as illustrated in a left part of FIG. 7.Thus, it is necessary to set the shallowest potential and the deepestpotential respectively at both ends of the electrode 85 and to form atransfer gradient. As a result, in a case where the charge accumulationunit (MEM) 72 as a whole is configured by the one electrode 85, an areaof an upper part of a transfer gradient in a waveform illustrated in theleft part of FIG. 7 is expressed as the number of saturation electronsQs.

On the other hand, in a case where the charge accumulation unit (MEM) 72has a laminated structure as indicated by the electrodes 81 to 83 inFIG. 6, it is possible to set a transfer gradient in each of theelectrodes 81 to 83 as illustrated in a right part of FIG. 7.Accordingly, as indicated by an arrow in the right part of FIG. 7, it ispossible to set a transfer gradient while serially performing switchingat a deep potential in each of the electrodes 81 to 83. As a result, asillustrated in the right part of FIG. 7, it becomes possible to increasethe number of saturation electrons Qs expressed as an area of an upperpart of a transfer gradient compared with a case illustrated in the leftpart of FIG. 7.

Note that a potential distribution between electrodes in a case where atransfer gradient of the charge accumulation unit (MEM) 72 is configuredby the one electrode 85 is illustrated in the left part of FIG. 7. Morespecifically, a potential distribution in the photoelectric conversionunit (PD) 71, the electrode 85, the transfer transistor 84, and thecharge voltage conversion unit (FD) 73 is illustrated from the left inthe left part of FIG. 7. In the left part of FIG. 7, since the transfergradient is configured only by the electrode 85, both end parts arerespectively set as the shallowest potential and the deepest potential.Thus, the potential distribution is monotonically decreased.

Similarly, a potential distribution between electrodes in a case where atransfer gradient of the charge accumulation unit (MEM) 72 is configuredby the electrodes 81 to 83 is illustrated in the right part of FIG. 7.More specifically, a potential distribution in the photoelectricconversion unit (PD) 71, the electrodes 81 to 83, the transfertransistor 84, and the charge voltage conversion unit (FD) 73 isillustrated from the left in the right part of FIG. 7. In the right partof FIG. 7, since a transfer gradient can be configured in each of theelectrodes 81 to 83 and the transfer transistor 84, it becomes possibleto set the transfer gradient at each deep potential. Thus, a potentialdistribution in which an increase and decrease are repeated in a deeppart in each of positions corresponding to the electrodes 81 to 83 isacquired.

Also, in a case where the charge accumulation unit (MEM) 72 has alaminated structure including the electrodes 81 to 83 illustrated inFIG. 6, terminals 81 a to 83 a respectively connected to the electrodes81 to 83 can be intensively provided on a column L2 (see FIG. 5)including charge voltage conversion units (FD) 73 and pixel transistors(Tr.) 74. Accordingly, it becomes possible to enhance an effect ofalight shielding film to prevent incidence to the charge accumulationunit (MEM) 72.

That is, as illustrated in FIG. 8, a light shielding film 101 isprovided in the charge accumulation unit (MEM) 72 in order to avoiddirect incidence of incident light. More specifically, as illustrated inan upper part of FIG. 8, this light shielding film 101 is provided insuch a manner as to cover the whole charge accumulation unit (MEM) 72.As illustrated in a lower part of FIG. 8, this light shielding film 101is provided to cover the charge accumulation unit (MEM) 72, an openingbeing provided and incidence of incident light being received in anupper part of the photoelectric conversion unit (PD) 71.

Note that a top view of charge accumulation units (MEM) 72 in two pixels51 is illustrated in the upper part of FIG. 8. It is illustrated thatelectrodes 81-1 to 83-1, a transfer transistor 84-1, terminals 81 a-1 to83 a-1, and a charge voltage conversion unit (FD) 73-1 are provided inthe pixel 51 on the left side. Also, it is illustrated that electrodes81-2 to 83-2, a transfer transistor 84-2, terminals 81 a-2 to 83 a-2,and a charge voltage conversion unit (FD) 73-2 are provided in the pixel51 on the right side.

Then, in the upper part of FIG. 8, a light shielding film 101 colored tocover the whole electrodes 81-1 to 83-1 and electrodes 81-2 to 83-2 isexpressed.

Also, a side sectional view of one pixel 51 is illustrated in the lowerpart of FIG. 8. It is illustrated that a photoelectric conversion unit(PD) 71, a charge accumulation unit (MEM) 72, and a charge voltageconversion unit (FD) 73 are provided from the left on a substrate 102.Also, it is illustrated that electrodes 81 to 83 are provided and atransfer transistor 84 is provided on the charge accumulation unit (MEM)72 serially from a side of the photoelectric conversion unit (PD) 71.Furthermore, it is illustrated that the electrodes 81 to 83 areprovided, and the light shielding film 101 is provided to cover thetransfer transistor 84.

On the other hand, in a case where an electrode shape for setting atransfer gradient in a charge accumulation unit (MEM) 72 is not theabove-described configuration in which a recess is provided at a centerand lamination is performed but is, for example, a structure such aselectrodes 91 to 93 and a transfer transistor 94 that are laminated in aplate-like manner as illustrated in an upper part of FIG. 9, terminals91 a to 94 a from the electrodes 91 to 93 and the transfer transistor 94are provided.

Here, as illustrated in the upper part of FIG. 9, a light shielding film111 is also formed on the charge accumulation unit (MEM) 72. In thiscase, the terminals 92 a and 93 a cannot be connected to a differentwiring line if being covered with the light shielding film 111. Thus, anopening 111 a is provided in the light shielding film 111 in order torealize electrical connection of a wiring line at the terminals 92 a and93 a.

Thus, as illustrated in a lower part of FIG. 9, there is a possibilitythat incident light enters from the opening 111 a, reaches the chargeaccumulation unit (MEM) 72, and generates a noise in the chargeaccumulation unit (MEM) 72 in which a charge transferred from aphotoelectric conversion unit (PD) is originally accumulated.

Accordingly, electrodes with a recess being provided at a center, suchas the electrodes 81 to 83 for generating a transfer gradient in thecharge accumulation unit (MEM) 72 in FIG. 6 are laminated. Thus, itbecomes possible to intensively provide terminals 81 a to 83 a on acolumn L2 (FIG. 5) including charge voltage conversion units (FD) 73 andpixel transistors (Tr.) 74 as illustrated in a part surrounded by adotted line in FIG. 6. As a result, since it is not necessary to providean opening for connecting the terminals 81 a to 83 a and a wiring lineas indicated with the light shielding film 101, it becomes possible toenhance an effect of the light shielding film 101 and to reducegeneration of a noise in the charge accumulation unit (MEM) 72.

Note that an example of using three electrodes in setting of a transfergradient in the charge accumulation unit (MEM) 72 has been described inthe above. However, the different number of electrodes may be used.Also, an example in which thicknesses of electrodes (gate length) aresubstantially even has been described as illustrated in FIG. 6. However,electrodes with uneven thickness (gate length) may be included. Here, athickness of an electrode (gate length) may be decreased and the numberof electrodes may be increased in a case where a transfer gradient isslightly insufficient. On the other hand, a thickness of an electrodemay be increased and the number of electrodes may be decreased in a casewhere there is a margin in a transfer gradient.

As described above, since a transfer of a charge in a chargeaccumulation unit (MEM) 72 can be formed in the shortest distance in alldirections according to a solid-state imaging element of the presenttechnology, transfer efficiency can be improved.

Also, it becomes possible to separately arrange a column ofphotoelectric conversion units (PD) 71 and a column including chargevoltage conversion units (FD) and pixel transistors (pixel Tr.) inparallel with each other in a case where pixels with the above-describedconfiguration are arranged in an array. Thus, it becomes possible tosimplify routing of a wiring line.

Furthermore, since the above-described structure in which a plurality ofelectrodes with a recess being provided at a center is laminated isincluded in a CIS, it becomes possible to bundle positions of taking outterminals in one direction. Thus, a degree of freedom in a layout of alight shielding film 101 provided on an upper layer of a chargeaccumulation unit (MEM) 72 is improved, and generation of a noise can bereduced by secure shielding of the charge accumulation unit (MEM) 72.

<Example of Application to Electronic Device>

The above-described solid-state imaging element can be applied tovarious electronic devices such as an imaging device such as a digitalstill camera or a digital video camera, a mobile phone having an imagingfunction, and a different device having an imaging function.

FIG. 10 is a block diagram illustrating a configuration example of animaging device as an electronic device to which the present technologyis applied.

An imaging device 201 illustrated in FIG. 10 includes an optical system202, a shutter device 203, a solid-state imaging element 204, a drivecircuit 205, a signal processing circuit 206, a monitor 207, and amemory 208 and can image a still image and a moving image.

The optical system 202 includes one or a plurality of lenses, guideslight (incident light) from a subject to the solid-state imaging element204, and forms an image on a light receiving surface of the solid-stateimaging element 204.

The shutter device 203 is arranged between the optical system 202 andthe solid-state imaging element 204, and controls a light emittingperiod and a light blocking period with respect to the solid-stateimaging element 204 under control by a drive circuit 1005.

The solid-state imaging element 204 includes a package including theabove-described solid-state imaging element in FIG. 4 and FIG. 6. Thesolid-state imaging element 204 accumulates a signal charge for acertain period according to light formed on the light receiving surfacevia the optical system 202 and the shutter device 203. The signal chargeaccumulated in the solid-state imaging element 204 is transferredaccording to a drive signal (timing signal) supplied from the drivecircuit 205.

The drive circuit 205 outputs a drive signal to control a transferoperation of the solid-state imaging element 204 and a shutter operationof the shutter device 203, and drives the solid-state imaging element204 and the shutter device 203.

The signal processing circuit 206 performs various kinds of signalprocessing on the signal charge output from the solid-state imagingelement 204. An image (image data) acquired by the signal processing bythe signal processing circuit 206 is supplied to and displayed by themonitor 207 or is supplied to and stored (recorded) in the memory 208.

In the imaging device 201 configured in such a manner, it becomes alsopossible to realize imaging with a low noise in all pixels byapplication of the solid-state imaging element in FIG. 4 and FIG. 6instead of the above-described solid-state imaging element 204.

<Example of Usage of Solid-State Imaging Element>

FIG. 11 is a view illustrating an example of usage of theabove-described solid-state imaging element in FIG. 4 and FIG. 6.

As described in the following, the above-described solid-state imagingelement in FIG. 4 and FIG. 6 can be used in various cases of sensinglight such as visible light, infrared light, ultraviolet light, or anX-ray.

A device of photographing an image which device is used for viewing andis, for example, a digital camera, or a mobile device with a camerafunction.

A device that is used for traffic and that is, for example, anin-vehicle sensor that photographs a front side, a back side,surroundings, or the inside of a car for safe driving such as automaticstopping or for recognition of a state of a driver, a monitoring camerathat monitors a driving vehicle or a road, or a ranging sensor thatmeasures a distance between vehicles.

A device used for a home electric appliance such as a TV, arefrigerator, or an air conditioner in order to photograph a gesture ofa user and to perform a device operation corresponding to the gesture.

A device, which is used for a medical service or a health care, such asan endoscope or a device that photographs a blood vessel by reception ofinfrared light.

A device, which is used for security, such as a monitoring camera forcrime prevention or a camera for recognizing a person.

A device, which is used for a beauty care, such as a skin measuringinstrument that photographs skin or a microscope that photographs ascalp.

A device, which is used for a sport, such as an action camera or awearable camera for a sport.

A device, which is used for agriculture, such as a camera for monitoringa state of a farm or a crop.

Note that the present technology may include the followingconfiguration.

(1) A solid-state imaging element including:

a pixel including

a photoelectric conversion unit that generates a charge by photoelectricconversion according to an amount of incident light,

a charge accumulation unit that accumulates the charge generated by thephotoelectric conversion unit, a charge voltage conversion unit thatconverts the charge accumulated in the charge accumulation unit intovoltage, and

a pixel transistor that outputs a pixel signal on the basis of thevoltage converted by the charge voltage conversion unit,

in which in a case where the charge voltage conversion unit is connectedto a center of the charge accumulation unit and pixels are arrayed in anarray, a column including photoelectric conversion units and a columnincluding voltage conversion units and pixel transistors are formed inparallel.

(2) The solid-state imaging element according to (1), further includinga plurality of electrodes that forms a transfer gradient to transfer thecharge accumulated in the charge accumulation unit,

in which a recess is provided at a center of each of the plurality ofelectrodes in such a manner as to face the charge voltage conversionunit, an electrode in an outermost periphery being formed in such amanner as to surround, in the recess, a different electrode smaller thanthe electrode in the outermost periphery, the different electrode beingformed in such a manner as to surround, in the recess, a differentelectrode smaller than the different electrode, and an electrodeconnected to the charge voltage conversion unit being formed in therecess of the smallest electrode.

(3) The solid-state imaging element according to (2), in whichthicknesses of the plurality of electrodes are even.

(4) The solid-state imaging element according to (2), in whichthicknesses of the plurality of electrodes are uneven.

(5) The solid-state imaging element according to (4), in which theplurality of electrodes is configured with a small number of thickelectrodes as a margin in the transfer gradient in the chargeaccumulation unit becomes large, and is configured with a large numberof thin electrodes as the transfer gradient becomes insufficient.

(6) An imaging device including:

a pixel including

a photoelectric conversion unit that generates a charge by photoelectricconversion according to an amount of incident light,

a charge accumulation unit that accumulates the charge generated by thephotoelectric conversion unit,

a charge voltage conversion unit that converts the charge accumulated inthe charge accumulation unit into voltage, and

a pixel transistor that outputs a pixel signal on the basis of thevoltage converted by the charge voltage conversion unit,

in which in a case where the charge voltage conversion unit is connectedto a center of the charge accumulation unit and pixels are arrayed in anarray, a column including photoelectric conversion units and a columnincluding voltage conversion units and pixel transistors are formed inparallel.

(7) An electronic device including:

a pixel including

a photoelectric conversion unit that generates a charge by photoelectricconversion according to an amount of incident light,

a charge accumulation unit that accumulates the charge generated by thephotoelectric conversion unit,

a charge voltage conversion unit that converts the charge accumulated inthe charge accumulation unit into voltage, and

a pixel transistor that outputs a pixel signal on the basis of thevoltage converted by the charge voltage conversion unit,

in which in a case where the charge voltage conversion unit is connectedto a center of the charge accumulation unit and pixels are arrayed in anarray, a column including photoelectric conversion units and a columnincluding voltage conversion units and pixel transistors are formed inparallel.

REFERENCE SIGNS LIST

-   51, 51-1 to 51-9 Pixel-   71 Photoelectric conversion unit (PD)-   72 Charge accumulation unit (MEM)-   73 Charge voltage conversion unit (FD)-   74 Pixel transistor (pixel Tr.)-   81 to 83 Electrode-   84 Transfer transistor-   81 a to 84 a, 81 a-1 to 84 a-1, 81 a-2 to 84 a-2 Terminal-   101, 111 Light shielding film-   111 a, 111 a-1 to 111 a-4 Opening

The invention claimed is:
 1. A solid-state imaging element, comprising:a pixel array comprising a plurality of pixels, wherein each pixel ofthe plurality of pixels comprises: a photoelectric conversion unitconfigured to generate a charge by photoelectric conversion based on anamount of incident light; a charge accumulation unit configured toaccumulate the charge generated by the photoelectric conversion unit; aplurality of electrodes configured to form a transfer gradient totransfer the charge accumulated in the charge accumulation unit; acharge voltage conversion unit configured to convert the accumulatedcharge into a voltage; and a pixel transistor configured to output apixel signal based on the voltage converted by the charge voltageconversion unit, wherein a plurality of connection terminals associatedwith the plurality of electrodes are in a column of the pixel array, andthe column comprises the charge voltage conversion unit and the pixeltransistor, and wherein a recess is at a center of each electrode of theplurality of electrodes, and the recess faces the charge voltageconversion unit.
 2. The solid-state imaging element according to claim1, wherein a first electrode, of the plurality of electrodes, in anoutermost periphery of the charge accumulation unit surrounds a secondelectrode of the plurality of electrodes which is smaller than the firstelectrode, wherein the second electrode surrounds a third electrode ofthe plurality of electrodes which is smaller than the second electrode,and wherein a fourth electrode connected to the charge voltageconversion unit is in the recess of the third electrode.
 3. Thesolid-state imaging element according to claim 2, wherein thicknesses ofthe plurality of electrodes are same.
 4. The solid-state imaging elementaccording to claim 2, wherein thicknesses of the plurality of electrodesare different.
 5. The solid-state imaging element according to claim 4,wherein at least one of a number of thick electrodes of the plurality ofelectrodes or a number of thin electrodes of the plurality of electrodesis based on the transfer gradient in the charge accumulation unit. 6.The solid-state imaging element according to claim 1, wherein the chargevoltage conversion unit is connected to a center of the chargeaccumulation unit, wherein a first column of the pixel array comprises aplurality of the photoelectric conversion units and a second column ofthe pixel array comprises a plurality of the voltage conversion unitsand a plurality of the pixel transistors, and wherein the first columnand the second column are non-overlapped.
 7. An imaging device,comprising: a pixel array comprising a plurality of pixels, wherein eachpixel of the plurality of pixels comprises: a photoelectric conversionunit configured to generate a charge by photoelectric conversion basedon an amount of incident light; a charge accumulation unit configured toaccumulate the charge generated by the photoelectric conversion unit; aplurality of electrodes configured to form a transfer gradient totransfer the charge accumulated in the charge accumulation unit; acharge voltage conversion unit configured to convert the accumulatedcharge into a voltage; and a pixel transistor configured to output apixel signal based on the voltage converted by the charge voltageconversion unit, wherein a plurality of connection terminals associatedwith the plurality of electrodes are in a column of the pixel array, andthe column comprises the charge voltage conversion unit and the pixeltransistor, and wherein a recess is at a center of each electrode of theplurality of electrodes, and the recess faces the charge voltageconversion unit.
 8. An electronic device, comprising: a pixel arraycomprising a plurality of pixels, wherein each pixel of the plurality ofpixels comprises: a photoelectric conversion unit configured to generatea charge by photoelectric conversion based on an amount of incidentlight; a charge accumulation unit configured to accumulate the chargegenerated by the photoelectric conversion unit; a plurality ofelectrodes configured to form a transfer gradient to transfer the chargeaccumulated in the charge accumulation unit; a charge voltage conversionunit configured to convert the accumulated charge into a voltage; and apixel transistor configured to output a pixel signal based on thevoltage converted by the charge voltage conversion unit, wherein aplurality of connection terminals associated with the plurality ofelectrodes are in a column of the pixel array, and the column comprisesthe charge voltage conversion unit and the pixel transistor, and whereina recess is at a center of each electrode of the plurality ofelectrodes, and the recess faces the charge voltage conversion unit.